The present invention relates to a pressure responsive potentiometer.
The present potentiometer has the property that the electrical resistance through the body of the potentiometer decreases when a pressure applied thereto increases.
One such pressure responsive potentiometer is described in Swedish Patent No. (patent application 8303840-6) Publication No. 456,042, dated Aug. 29, 1988. This patent specification describes a pressure responsive potentiometer embodiment in which the body is cylincrical and disc-shaped and comprises a mixture of a pastic substance and carbon powder. According to one specified embodiment, the body comprises 50% silicon mass and 50% carbon powder.
Corresponding bodies are also known from other patent specifications, of which the U.S. Pat. No. 4,273,682 is one.
The aforesaid Swedish patent specification mentions the use of carbon powder, such as pulverized graphite or pulversized black coal. The U.S. Pat. No. 4,273,682 also mentions carbon powder of fine fractions, i.e. of a size corresponding to Tyler's 80-mesh sieve, and still finer. An 80-mesh sieve is a sieve having 80 meshes per inch. Consequently, grains or particles capable of passing through the sieve have a diameter corresponding to one eightieth of an inch, i.e. approximately 0.3 mm.
The known technique thus teaches the use of carbon powder or very fine carbon grains. U.S. Pat. No. 4,273,682 recommends the use of screens of 80 mesh to 325 mesh, i.e. corresponding to a diameter from approximately 0.3 mm to 0.08 mm.
When using the device according to the aforesaid Swedish patent specification, it was found the reproducibility with regard to the resistance through the body against applied pressure was not acceptable. This problem was particularly manifest in applications where several of the devices were used and were each of said devices were intended to have the same or at least very similar properties.
In addition to the problem of reporducibility, it was found that the relationship between applied pressure and resistance through the body did not always follow an even and continuous relationship, but instead a relationship which varied greatly and at times discontinuously.
Subsequent to compreshensive inventive work and experiments, it has been possible to eliminate these undesirable properties.